In manufacturing automobiles or the like, a window glass having a complicated three-dimensional shape has been used from demands on design and aerodynamics etc. in recent years. When an object is seen through such window glass with a three-dimensionally curved plane, the object is sometimes seen to have a distortion. This phenomenon is called a perspective distortion phenomenon, and it is known that the phenomenon is caused at a non-parallel portion or a curved plane portion in a glass sheet. Since the perspective distortion is a factor of hindering visibility, in particular, in driving an automobile, the permissible maximum value of the perspective distortion is ruled in JIS (Japanese Industrial Standards).
The perspective distortion is evaluated by inspecting the optical performance of an intended glass sheet, or examining sensually an intended glass sheet. In recent years, there is a technique of evaluating the perspective distortion based on a model of three-dimensional shape of a glass sheet produced by CAD (Computer Aided Design), instead of the conventional optical performance test or sensory examination.
These conventional evaluation methods evaluate the perspective distortion in a case that a stationary object is seen through a glass sheet (hereinbelow, referred to as the static perspective distortion). Accordingly, it is suitable in a case of evaluating the perspective distortion of a glass sheet used for a building. However, a problem would arise in a case of evaluating the perspective distortion of a glass sheet used for a movable body such as an automobile.
Namely, the evaluation of the static perspective distortion is as a result of evaluating the perspective distortion at a large number of points in a local portion of the glass sheet independently, and it is not as a result of considering the continuity of the perspective distortion between a plurality of points. Accordingly, in a glass sheet wherein the perspective distortion of each local portion satisfies a predetermined prescribed value, there is a case that a change of the perspective distortion between adjacent local portions is large. In such case, when a scenery outside the movable body is seen through such glass sheet, the perspective distortion of an image changes largely with the movement of the movable body, and undulation is recognized.
The important inspection item of a movable body such as an automobile is, in addition to evaluating the static perspective distortion of an object in a stationary state when it is seen through a glass sheet, to evaluate the perspective distortion of the object seen through the glass sheet in a state of being driven (hereinbelow, referred to as the dynamic perspective distortion).
Further, in recent years, a technique of designing a three-dimensional shape of a glass sheet by CAD has widely been used. Accordingly, it is desirable to optimize the shape of the glass sheet in consideration of an evaluation result of the dynamic perspective distortion at the stage of designing.
The present invention has been achieved in consideration of the above-mentioned circumstances, and it is a primary object to provide a method for evaluating the dynamic perspective distortion of an object in a case that a scenery outside the movable body is seen through a transparent body such as glass. Further, it is secondary object of the present invention to provide a method for determining a three-dimensional shape of a transparent body based on an evaluation result of the dynamic perspective distortion.